This seems insufficient. To properly test SMTP settings, you should at least do an RCPT TO with some external email address (ex. postmaster@example.com), but bail out before sending DATA. This will actually test that you have relay permissions, in effect validating your username/password and/or client certificate.
– Jonathan AmendSep 18 '14 at 16:10

there is a infinite loop in SmtpConnectorWithoutSsl . In CheckResponse method the line while (_socket.Available == 0) should have a limit. I hit a scenario where _socket.Available was never going to equal anything other than 0. but, aside from that - this works perfect. been using it for about 6 months without issue.
– Heriberto LugoDec 29 '17 at 17:36